filechooserbutton: Update the button/combo at construction time
filechooserbutton: Update the button/combo at construction time

This way the internal labels will show the correct selection even if nothing
has been selected programmatically.

Signed-off-by: Federico Mena Quintero <4999915a961edfd7686112c2935288e1266eae14@gnome.org>

Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2